Complete androgen insensitivity caused by a splice donor site mutation in intron 2 of the human androgen receptor gene resulting in an exon 2-lacking transcript with premature stop-codon and reduced expression

Treatments Targeting the Androgen Receptor and Its Splice Variants in Breast Cancer

Breast cancer is a major cause of death worldwide. The complexity of endocrine regulation in breast cancer may allow the cancer cells to escape from a particular treatment and result in resistant and aggressive disease. These breast cancers usually have fewer treatment options. Targeted therapies for cancer patients may offer fewer adverse side effects because of specificity compared to conventional chemotherapy. Signaling pathways of nuclear receptors, such as the estrogen receptor (ER), have been intensively studied and used as therapeutic targets. Recently, the role of the androgen receptor (AR) in breast cancer is gaining greater attention as a therapeutic target and as a prognostic biomarker. The expression of constitutively active truncated AR splice variants in breast cancer is a possible mechanism contributing to treatment resistance. Therefore, targeting both the full-length AR and AR variants, either through the activation or suppression of AR function, depending on the status of the ER, progesterone receptor, or human epidermal growth factor receptor 2, may provide additional treatment options. Studies targeting AR in combination with other treatment strategies are ongoing in clinical trials. The determination of the status of nuclear receptors to classify and identify patient subgroups will facilitate optimized and targeted combination therapies.

Identification of two additional novel mutations in the AR gene associated with severe forms of androgen insensitivity syndrome

The Androgen insensitivity syndrome (AIS) in its complete form (CAIS) is a disorder in abnormal male development characterized by a complete female phenotype in a 46,XY individual. The most frequent cause of this disorder is a hemizygous mutation in androgen receptor (AR) gene located in X chromosome. The first aim of this study was to confirm the clinical diagnosis in a series of Tunisian patients with a typical phenotype of CAIS by molecular genetic analysis. The second aim was to determine the AR mutational profile in the local population. The entire coding region and the exon-intron junctions of the AR gene were sequenced in a series of ten patients. AR defects were found in nine patients. Despite the small number of cases, two of the nine identified mutations were novel. The first novel mutation was an 8-bp deletion in exon 1 (c.862_869del) resulting in a frameshift (p.A288Qfs*14). The second was a splice site mutation c.1885 + 1G > T (IVS3 + 1G > T). In this study, genetic testing has confirmed the diagnosis of most CAIS patients and has revealed two novel mechanisms responsible for the pathogenesis of AIS, as well as seven other reported mutations.

Features of the fetal gonad in androgen synthesis in the postpubertal testis are preserved in complete androgen insensitivity syndrome due to a novel genetic splice site donor variant in androgen receptor gene intron 1

Mutations in the X-linked androgen receptor (AR) gene cause complete androgen insensitivity syndrome (CAIS). CAIS may cause congenital sexual development disorder, which frequently develops into testicular tumors. Here, we describe a novel splice-site intron 1 mutation in AR leading to improper splicing and AR protein absence in CAIS gonads. We characterized a patient's postpubertal gonadal steroidogenic enzyme expression profile. Localization of both CYP11A1 and CYP17A1 enzymes was restricted to both Leydig tumor cells and adjacent to tumor gonadal tissues. Sertoli cells of the CAIS gonad showed abundant HSD17B3 protein, which is an adult Leydig cell marker that enables the conversion of androstenedione to testosterone. Such HSD17B3 expression is typical for fetal-type Sertoli cells in rodents. The postpubertal CAIS gonad of our patient was completely devoid of androgen signaling pathway activity. Plausibly, the postpubertal Leydig cells consisted of two distinct cell populations: postpubertal fetal-type Leydig cells that persisted as androgen-independent cells and immature adult Leydig cells that failed to differentiate. Taken together, in this CAIS postpubertal testis, both Leydig and fetal-type Sertoli cells participated in testosterone production. Our results indicate the importance of molecular analysis as well as the characterization of steroidogenic enzyme profiling in the CAIS patient's gonad.

Characterization and expression of androgen receptors in olive flounder

Androgens are critical hormones that regulate sex differentiation, sexual maturation, and spermatogenesis in vertebrates, which is mainly mediated by androgen receptors (ARs). Reports on transcript variants of ar (AR encoding gene) in human are almost always associated with cancers and androgen insensitivity syndrome. However, the knowledge of ar variants in teleosts is scarce. In this study, arβ and two transcript variants of arα (arα1 and arα2) in olive flounder (Paralichthys olivaceus) were cloned and analyzed. Their expression patterns were investigated in 16 adult female and male tissues by RT-PCR, respectively. arα1 was expressed in the majority of tissues excluding male liver, medulla oblongata and female cerebellum, with higher levels in male gonad, kidney, head kidney, intestine, stomach, spleen, heart and gill than in female. arα2 had similar expression patterns as arα1, with lower levels in general. arβ was also widely expressed in various tissues excluding male spleen, female spleen and gill, with higher levels in male gonad, kidney, head kidney, intestine and lower levels in hypothalamus than in female. Compared with arβ, much lower expression levels of arα1 and arα2 were detected in different brain areas. The real-time quantitative PCR (qPCR) results showed that the total arα expression level was relatively higher during olive flounder gonadal differentiation and before the onset of testis differentiation, whereas arβ was expressed significantly higher during male gonadal differentiation period than female gonadal differentiation period. The in vitro transient transfection assays showed that ARα1, ARα2 and ARβ could all suppress the activity of cyp19a (p450arom aromatase gene) promoter, and the inhibitory effect of ARα1 was dose dependent. Our results imply that arα1, arα2 and arβ are sex-related genes and they might play important roles in gonadal differentiation in flounder.

Fish granulocytes express a constitutively active androgen receptor variant

In humans, alternative splicing of androgen receptor (AR) is usually involved in some diseases. However, our knowledge about the presence of AR variants in other species and its importance for immunity is scant. Here, we report the identification of a constitutively active AR variant lacking the ligand-binding domain (LBD), ARΔLBD, in the fish gilthead seabream. ARΔLBD is expressed in the testis and the head-kidney (HK), and its expression varies with the reproductive stage and is correlated with plasma testosterone (T). In addition, ARΔLBD is expressed in acidophilic granulocytes (AGs), which are the functional equivalent of mammalian neutrophils, but not in macrophages, and its expression is modulated by both T and immune stimuli. Notably, AR and ARΔLBD were able to interact, being the activity of AR dominant at all concentrations tested of the ligand. These results reveal a new mechanism for the regulation of neutrophil biology in vertebrates and explain the conflicting results that suggest that androgens are less important than AR in human and mouse neutrophil homeostasis.

Alternative splicing in cancer: implications for biology and therapy

Alternative splicing has critical roles in normal development and can promote growth and survival in cancer. Aberrant splicing, the production of noncanonical and cancer-specific mRNA transcripts, can lead to loss-of-function in tumor suppressors or activation of oncogenes and cancer pathways. Emerging data suggest that aberrant splicing products and loss of canonically spliced variants correlate with stage and progression in malignancy. Here, we review the splicing landscape of TP53, BARD1 and AR to illuminate roles for alternative splicing in cancer. We also examine the intersection between alternative splicing pathways and novel therapeutic approaches.

Identification of androgen receptor variants in testis from humans and other vertebrates

The androgen receptor (AR) is a ligand-activated transcription factor member of the nuclear receptor superfamily. The existence of alternatively spliced variants is well recognised for several members of this superfamily, most of them having functional importance. For example, several testicular oestrogen receptor variants have been suggested to play a role in the regulation of spermatogenesis. However, information on AR variants is mostly related to cancer and androgen insensitivity syndrome (AIS) cases. The objective of this study was to investigate the expression of AR variants in the testis from humans and other vertebrates. Four AR variants [ARΔ2(Stop) , ARΔ2(23Stop) , ARΔ3 and ARΔ4(120)] were identified in human testis. ARΔ2(Stop) and ARΔ3, with exon 2 or 3 deleted, respectively, were also expressed in human liver, lung, kidney and heart. In addition, ARΔ2(Stop) was expressed in rat and gilthead seabream testis, while an ARΔ3 was detected in African clawed frog testis. This is the first report revealing the existence of AR variants in the testis of evolutionarily distant vertebrate species and in nonpathological tissues. These data suggest the functional importance of these novel AR forms and demonstrate a complexity in AR signalling that is not exclusive of pathological conditions.

Alternatively spliced androgen receptor variants

Alternative splicing is an important mechanism for increasing functional diversity from a limited set of genes. Deregulation of this process is common in diverse pathologic conditions. The androgen receptor (AR) is a steroid receptor transcription factor with functions critical for normal male development as well as the growth and survival of normal and cancerous prostate tissue. Studies of AR function in androgen insensitivity syndrome (AIS) and prostate cancer (PCa) have demonstrated loss-of-function AR alterations in AIS and gain-of-function AR alterations in PCa. Over the past two decades, AR gene alterations have been identified in various individuals with AIS, which disrupt normal AR splicing patterns and yield dysfunctional AR protein variants. Recently, altered AR splicing patterns have been identified as a mechanism of PCa progression and resistance to androgen depletion therapy. Several studies have described the synthesis of alternatively spliced transcripts encoding truncated AR isoforms that lack the ligand-binding domain, which is the ultimate target of androgen depletion. Many of these truncated AR isoforms function as constitutively active, ligand-independent transcription factors that can support androgen-independent expression of AR target genes, as well as the androgen-independent growth of PCa cells. In this review, we will summarize the various alternatively spliced AR variants that have been discovered, with a focus on their role and origin in the pathologic conditions of AIS and PCa.

Androgens and spermatogenesis: lessons from transgenic mouse models

Transgenic mouse models have contributed considerably to our understanding of the cellular and molecular mechanisms by which androgens control spermatogenesis. Cell-selective ablation of the androgen receptor (AR) in Sertoli cells (SC) results in a complete block in meiosis and unambiguously identifies the SC as the main cellular mediator of the effects of androgens on spermatogenesis. This conclusion is corroborated by similar knockouts in other potential testicular target cells. Mutations resulting in diminished expression of the AR or in alleles with increased length of the CAG repeat mimick specific human forms of disturbed fertility that are not accompanied by defects in male sexual development. Transcriptional profiling studies in mice with cell-selective and general knockouts of the AR, searching for androgen-regulated genes relevant to the control of spermatogenesis, have identified many candidate target genes. However, with the exception of Rhox5, the identified subsets of genes show little overlap. Genes related to tubular restructuring, cell junction dynamics, the cytoskeleton, solute transportation and vitamin A metabolism are prominently present. Further research will be needed to decide which of these genes are physiologically relevant and to identify genes that can be used as diagnostic tools or targets to modulate the effects of androgens in spermatogenesis.

Tissue-selective knockouts of steroid receptors: a novel paradigm in the study of steroid action

The use of tissue-selective rather than ubiquitous knockouts of steroid receptors allows a more refined study of the mechanism of steroid action in defined target tissues and circumvents problems such as early lethality or major developmental defects precluding studies in affected organs. In this chapter, we describe the main steps involved in the development of tissue-selective steroid receptor knockouts by Cre/loxP technology. Problems in the development of a mouse strain with a floxed receptor allele, the selection of a suitable Cre expressing mouse strain, the generation of cell-selective knockouts by crossbreeding of the mentioned mouse strains, and the control of appropriate receptor inactivation are discussed taking the generation of mice with a Sertoli cell-selective ablation of the androgen receptor as an example.

A splicing variant of the androgen receptor detected in a metastatic prostate cancer exhibits exclusively cytoplasmic actions

The androgen receptor (AR) is a ligand-activated transcription factor that displays genomic actions characterized by binding to androgen-response elements in the promoter of target genes as well as nongenomic actions that do not require nuclear translocation and DNA binding. In this study, we report exclusive cytoplasmic actions of a splicing variant of the AR detected in a metastatic prostate cancer. This AR variant, named AR23, results from an aberrant splicing of intron 2, wherein the last 69 nucleotides of the intronic sequence are retained, leading to the insertion of 23 amino acids between the two zinc fingers in the DNA-binding domain. We show that the nuclear entry of AR23 upon dihydrotestosterone (DHT) stimulation is impaired. Alternatively, DHT-activated AR23 forms cytoplasmic and perinuclear aggregates that partially colocalize with the endoplasmic reticulum and are devoid of genomic actions. However, in LNCaP cells, this cytoplasmic DHT-activated AR23 remains partially active as evidenced by the activation of transcription from androgen-responsive promoters, the stimulation of NF-kappaB transcriptional activity and by the decrease of AP-1 transcriptional activity. Our data reveal novel cytoplasmic actions for this splicing AR variant, suggesting a contribution in prostate cancer progression.

Phylogenetic conservation of the androgen receptor AR45 variant form in placental mammals

A cDNA coding for a tissue-specific AR45 variant form of the androgen receptor (AR) has recently been identified in humans, with highest expression levels found in heart. The deduced protein comprises the DNA-binding domain, hinge region and ligand-binding domain of the AR, but not the N-terminal domain which is replaced by a unique, short, seven amino-acid-long stretch. This sequence is encoded by the mutually exclusive exon 1B, located between exons 1 and 2 of the human AR gene. As transcript variants of the steroid receptor family have been shown to have important implications for hormone function, we set out to analyse the genomes of different organisms for potential AR45 expression. We found exon 1B to be conserved in the syntenic chromosomal region of non-human primates such as the chimpanzee Pan troglodytes, the orang-utan Pongo pygmaeus, the macaque Macaca mulatta and the marmoset Callithrix jacchus, and of the elephant Loxondonta africana, the pig Sus scrofa and the dog Canis familiaris. Quantification of AR45 transcript levels in heart, skeletal muscle and lung of Macaca fascicularis showed the heart to be the main organ of expression. A complete AR45 cDNA was furthermore isolated from the heart of this species. Comparative analysis of the identified AR45 exon 1B regions and of the deduced amino acids revealed a high conservation among species. The four N-terminal residues were identical in all eight species, whereas a few changes were seen in the other three residues in the marmoset, elephant and pig. In contrast, we observed more divergence in the mouse Mus musculus and rat Rattus norvegicus syntenic regions. Here a stop codon was found downstream of the potential start codon in the putatively deduced protein sequence and it can be inferred that no protein corresponding to AR45 exists in these two species. The existence of AR45 in different placental mammals with the exception of mouse and rat suggests a disappearance in rodents late in evolution, before the separation of the mouse and rat lineages, about 16 million years ago. In view of the potential function of AR45 as a regulator of AR function, and considering the multiple roles of androgens in normal physiology and in several diseases, these findings have important implications with regard to subtle differences in the action of the male sexual hormone in various organisms.

Molecular features and clinical phenotypes in androgen insensitivity syndrome in the absence and presence of androgen receptor gene mutations

Androgen insensitivity syndrome (AIS) is characterized by deficient or absent virilization in 46,XY individuals despite normal or even elevated androgen levels. AIS is usually caused by mutations in the androgen receptor (AR) gene. We aimed at contrasting clinical, biochemical, and molecular genetic characteristics of three patients (P1-P3) with clinically evident partial (P1) and complete (P2, P3) AIS with and without AR gene mutations. AR expression was studied in cultured genital skin fibroblasts (GSF) by Western immunoblotting, ligand binding analyses, Northern blotting, semiquantitative reverse transcription-polymerase chain reaction (RT-PCR), and RT-PCR spanning exons 1-8. AR gene DNA sequence was analyzed by single-strand conformation analysis (SSCA), and DNA sequencing. GSF revealed reduced (P1) or absent (P2, P3) ligand binding. Northern blots showed either slightly reduced hybridization of the 10.5-kb AR transcript (P3) or no hybridization (P1, P2), as confirmed by semiquantitative RT-PCR. RT-PCR spanning exons 1-8 detected single AR mRNA bands in P1-P3 excluding splicing errors. Western analyses showed either low (P1) or no (P2, P3) AR protein. While SSCA initially did not reveal any molecular abnormality, sequencing showed a novel CAG (Gln) to TAG (stop) mutation at codon 59 (P3) and a previously described 2-bp deletion at codon 472, leading to a frameshift and premature stop in codon 499 (P2). Intriguingly, P1 showed an unaltered DNA sequence of the coding region of the AR gene including all intron-exon boundaries. In conclusion, patients with clinically evident complete AIS are likely to harbor an AR gene mutation, demanding that the two polymorphic regions must always be included in molecular analyses of the AR gene. Moreover, our data support the concept that in a subset of AIS patients, particularly those with partial AIS, molecular alterations outside the coding region of the AR gene must be presumed.

Allele-specific transcript isoforms in human

Estimates of the number of human genes that produce more than one transcript isoform through alternative mRNA splicing depend on the assumption that the observation of multiple transcripts from a gene can be attributed entirely to alternative splicing. It is possible, however, that a substantial proportion of cases where multiple transcripts have been observed for a gene result from differences between alleles. Many examples of genes that are spliced differently from different alleles have been reported but no systematic estimate of the proportion of alternatively spliced genes that are affected by such polymorphisms has been carried out. We find that alternative transcript isoforms are non-randomly associated with closely linked nucleotide polymorphisms, based on an integrated analysis of the dbSNP, dbEST and ASAP databases. From the observed level of association between transcript isoforms and polymorphisms, we estimate that 21% of alternatively spliced genes are affected by polymorphisms that either completely determine which form of the transcript is observed or alter the relative abundances of some of the alternative isoforms. We provide a conservative lower bound of 6% on this estimate and point out that alternative splicing cannot be confirmed absolutely unless more than one transcript is observed from the same allele.

A Sertoli cell-selective knockout of the androgen receptor causes spermatogenic arrest in meiosis

Androgens control spermatogenesis, but germ cells themselves do not express a functional androgen receptor (AR). Androgen regulation is thought to be mediated by Sertoli and peritubular myoid cells, but their relative roles and the mechanisms involved remain largely unknown. Using Cre/loxP technology, we have generated mice with a ubiquitous knockout of the AR as well as mice with a selective AR knockout in Sertoli cells (SC) only. Mice with a floxed exon 2 of the AR gene were crossed with mice expressing Cre recombinase ubiquitously or selectively in SC (under control of the anti-Müllerian hormone gene promoter). AR knockout males displayed a complete androgen insensitivity phenotype. Testes were located abdominally, and germ cell development was severely disrupted. In contrast, SC AR knockout males showed normal testis descent and development of the male urogenital tract. Expression of the homeobox gene Pem, which is androgen-regulated in SC, was severely decreased. Testis weight was reduced to 28% of that in WT littermates. Stereological analysis indicated that the number of SC was unchanged, whereas numbers of spermatocytes, round spermatids, and elongated spermatids were reduced to 64%, 3%, and 0% respectively of WT. These changes were associated with increased germ cell apoptosis and grossly reduced expression of genes specific for late spermatocyte or spermatid development. It is concluded that cell-autonomous action of the AR in SC is an absolute requirement for androgen maintenance of complete spermatogenesis, and that spermatocyte/spermatid development/survival critically depends on androgens.

Homozygous single nucleotide polymorphism of the complement C1QA gene is associated with decreased levels of C1q in patients with subacute cutaneous lupus erythematosus

We report an association between a non-familial form of photosensitive Lupus-specific skin disease, subacute cutaneous lupus erythematosus (SCLE), and a new single nucleotide polymorphism (SNP) in the C1QA gene. We also describe an association between this SNP and lower levels of serum C1q. This SNP consists of adenine replacing the third guanine in the codon for aminoacid residue Gly70 (position excludes the 22 amino acid leading peptide) that is located in the second exon of the C1QA gene. We have designated this SNP C1qA-Gly70GGA (the GenBank sequence at this location is C1qA-Gly70GGG). A survey of 19 SCLE patients showed that 11 (58%) were homozygous for C1qA-Gly70GGA SNP, seven (37%) were heterozygous, and only one patient (5%) was homozygous for the GenBank sequence. In contrast, only 13 of 62 (21%) normal controls were homozygous for the C1qA-Gly70GGA SNP, 41 (66%) controls were heterozygous and eight (13%) controls were homozygous for the GenBank sequence. Thus, the C1qA-Gly70GGA SNP is strongly associated with SCLE (P-value = 0.005 by chi-square analysis with Yates correction). This SNP would traditionally be classified as clinically silent as it does not encode a different amino acid. However, our studies have suggested that this SNP appears to be associated with a functional abnormality of C1q expression since its presence correlates inversely with serum levels of C1q antigenic protein in both SCLE patients and normal controls. The mechanism by which this phenotypic change is associated with the translationally silent (synonymous) ClqA-Gly70GGA genetic variation is currently unknown.

A unique exonic splicing mutation in the human androgen receptor gene indicates a physiologic relevance of regular androgen receptor transcript variants

In a patient with partial androgen insensitivity syndrome (AIS), we identified a single inherited presumably silent nucleotide variation (AGC -> AGT) in exon 8 (codon 888) of the AR gene. However, in the patient's genital skin fibroblasts, a considerably shortened transcript of 5.5 kb (normal: 10.5 kb) was detected, which misses a part of exon 8 and a prominent portion of the 3'-untranslated region. The translation product includes eight missense amino acids from codon 886 onward followed by a premature stop codon. As shown by in vitro expression analysis, the mutant protein lacks any residual function. However, reverse transcribed PCRs and sequence data indicate the existence of two additional splicing variants of 6.4 kb and 7.8-kb length both in patient and normal control genital skin fibroblasts. These splicing variants comprise the complete coding region but a shortened 3'-untranslated region. Thus, a distinct alternative pre-messenger RNA-processing event leading to two additional transcripts occurs generally in genital skin fibroblasts. In addition, this process partially prevents aberrant splicing in the patient and produces a small fraction of normal, functionally intact AR-protein that could explain the partial masculinization in this patient. This first report of an exonic splicing mutation in the AR-gene indicates a physiologic relevance of the regular AR-messenger RNA variants with shortened 3'-untranslated regions and their functional translation products in human genital development.

Transcription of androgen receptor and 5alpha-reductase II in genital fibroblasts from patients with androgen insensitivity syndrome

Impaired virilisation during embryonic development and pubertal arrest in patients with androgen insensitivity syndromes (AIS) is usually caused by mutations in the androgen receptor (AR)- or the 5alpha-reductase II (5RII) gene. However, identical mutations may lead to strikingly different phenotypes. To investigate whether this may be caused by individually altered transcription rates in fibroblasts from the genital region (GF) from affected patients, we applied competitive reverse transcribed PCRs (competitive RT-PCR) targeting AR- and 5RII-transcripts. We could demonstrate that AR- and 5RII-mRNA concentrations in cells from patients with partial and complete AIS and missense mutations in the AR- or 5RII-gene are normal or only moderately lowered compared to equally aged normal controls. However, in a patient bearing a premature stop-codon in the AR-gene a considerably lowered AR-transcript level was detected. We conclude, that in patients with incomplete virilisation disorders due to missense mutations, transcription regulation of AR and 5RII generally follows normal patterns. Accordingly, the premature stop-codon found in one patient's AR-gene may rather cause reduced transcript stability than an impairment of transcription activity. Therefore, altered AR- and 5RII-transcription rates in fibroblasts from the GF do not seem to be the cause for the variable genotype-phenotype correlation in androgen insensitivity syndrome.

Novel point mutation in the splice donor site of exon-intron junction 6 of the androgen receptor gene in a patient with partial androgen insensitivity syndrome

Androgen receptor (AR) gene mutations have been shown to cause androgen insensitivity syndrome with altered sexual differentiation in XY individuals, ranging from a partial insensitivity with male phenotype and azoospermia to a complete insensitivity with female phenotype and the absence of pubic and axillary sexual hair after puberty. In this study we present an 11-yr-old XY girl, with clinical manifestations peculiar for impaired androgen biological action, including female phenotype, blind-ending vagina, small degree of posterior labial fusion, and absence of uterus, fallopian tubes, and ovaries. At the time of the diagnosis the patient had a FSH/LH ratio according to the puberal stage, undetectable 17beta-estradiol, and high levels of testosterone (80.1 ng/mL). After bilateral gonadectomy, performed at the age of 11 yr, histological examination showed small embryonic seminiferous tubules containing prevalently Sertoli cells and occasional spermatogonia together with abundant fibrous tissue. Molecular study of the patient showed a guanine to thymine transversion in position +5 of the donor splice site in the junction between exon 6 and intron 6 of the AR gene. The result of RT-PCR amplification of the AR messenger ribonucleic acid from cultured genital skin fibroblasts of the patient suggests that splicing is defective, and intron 6 is retained in most of the receptor messenger ribonucleic acid molecules. We show by immunoblotting that most of the expressed protein lacks part of the C-terminal hormone-binding domain, and a small amount of normal receptor is observed. This is probably responsible for the reduced binding capacity in genital skin fibroblasts of the patient. The molecular basis of the alteration in this case is a novel, uncommon mutation, leading to a phenotype indicative of a partial androgen insensitivity syndrome, Quigley's grade 5.